1. Field of the Invention
The invention relates to a method of making iron foil by electrodeposition, wherein in an electrochemical cell having a non-soluble anode iron is deposited from an acid electrolyte onto a moving cathode, and the iron deposited onto the cathode is removed in the form of a foil.
2. Description of the Prior Art
Such a method is known from the article "Electrolytic Iron Foil" by P. K. Subramanyan and W. M. King in "PLATING AND SURFACE FINISHING" of February 1972, pages 48 through 51. According to that article in principle the following reactions occur: EQU at the cathode: Fe.sup.2+ +2e.sup.- .fwdarw.Fe (foil) (I) EQU at the anode: 2Fe.sup.2+ .fwdarw.2Fe.sup.3+ +2e.sup.- (IV) EQU in the regenerator: 2Fe.sup.3+ +Fe.fwdarw.3Fe.sup.2+ (V)
A disadvantage of the known method, already indicated in the said article, is the simultaneous occurrence of the reaction: EQU in the regenerator: Fe+2H.sup.+ Fe.sup.2+ +H.sub.2 (III)
As a result of this, more Fe.sup.2+ ions are dissolved in the electrolyte than are deposited. The surplus Fe.sup.2+ ions have to be drained off A more serious problem is that the pH of the electrolyte increases because of the consumption of hydrogen ions so that Fe(OH).sub.3 deposition occurs.
In order to solve this problem Belgian patent BE No. 8700832 describes use of two levels of temperature, the electrodeposition in the case of an electrolyte based on iron chloride, and a low temperature for the regeneration of the electrolyte. This suppresses reaction (III). However, the problem with this process is that before regeneration the electrolyte has to be cooled and then after regeneration re-heated. This takes a great deal of energy which is not acceptable for a product whose cost price already consists for a large part of energy costs.
In order to solve this problem, Japanese patent application Nos. JP-A No. 61-111159 and JP-A No. 61-111160 as well as BE No. 8700832 mentioned above propose adding an organic substance to the electrolyte, the effect of which is likewise suppression of reaction (III).
However, a problem with the prior art practice discussed above is that the electrodeposition relies on the reactions (I), (IV) and (V). Because of the presence of Fe.sup.3+ ions in the electrolyte, the following reaction occurs at the cathode: EQU Fe(foil)+2Fe.sup.3+ .fwdarw.3Fe.sup.2+ (VI)
The result is that iron foil already deposited goes back into solution so that the output of the electrodeposition process is reduced. In order to suppress this reaction as much as possible, the electrolyte circulation through the regenerator is increased in order to keep the concentration of Fe.sup.3+ ions in the electrolyte at a low level. However, much pumping energy is needed for this circulation which, for the above-mentioned reason, is not acceptable.